For performing tests on devices under test, especially for measuring on individual devices on a wafer, the devices are usually contacted by using a probe comprising measuring tips. The probe is moved with regard to the device under test. The measuring tips contact contact pads on the surface of the device under test of the wafer. Now, a measurement can be performed. Such a measuring system is shown in the European patent application EP 2 840 598 A1.
Exemplary probes are shown in the documents U.S. Pat. Nos. 7,795,889 B2, 7,764,072 B2 and 7,786,741 B2.
When performing measurements on the device under test, it is important to know the exact power level of the measuring signal supplied to the device under test. An accurate power measurement usually though cannot be performed by the network analyzer performing the measurement. A dedicated power sensor is usually used. For example, the documents U.S. Pat. Nos. 6,741,070 B2, 7,705,582 B2 and 6,767,129 B2 show power measurement cells as used in such dedicated power sensors. Moreover, document DE 10 2008 057 607 A1 also shows an exemplary power measurement cell.
In order to determine the power level of the signal generated, for example by a network analyzer to be supplied to the device under test, usually the measuring probe is detached from the measuring device. The measuring device is then connected to the power sensor. The measuring device then generates the measuring signal and supplies it usually via coaxial cable to the power sensor, which determines the power of the measuring signal. Afterwards, the probe is reattached and measurements are performed with a now known power level. In order to increase accuracy, it is possible to model an influence of the probe on the measuring signal and accordingly modify the measuring signal.
Performing the above-mentioned process though requires a great deal of effort, since the detaching of the probe, the attaching of the power sensor and the reattaching of the probe are steps, which have to be performed manually and cannot be automated. Therefore, the step of performing a power calibration usually is only performed once at the beginning of a measurement series and not repeated later on. This leads to possibly inaccurate measuring results.
Also, the model based compensation of the influence of the measuring probe is notoriously inaccurate.
Accordingly, one object of the invention among others is to provide a measuring system and a measuring method, which allow for an accurate power calibration directly at the point at which the device under test is measured.
Also, another object of the invention is to achieve a low handling effort for the operator.